1. Field of the Invention
The present invention relates to a magnetoresistance effect element for reading a magnetic field intensity as a signal in a magnetic recording medium and the like.
A highly practical magnetoresistance effect element is required to have a large resistance change in a small external magnetic field. The magnetoresistance effect element of the present invention has a large resistance change in a small external magnetic field and can be practically used.
2. Description of the Related Art
In these years, a sensitivity of a magnetic sensor and a density of magnetic recording have been increased. With such increase, a magnetoresistance effect magnetic sensor (hereinafter referred to as "MR sensor") and a magnetoresistance effect magnetic head (hereinafter referred to as "MR head") have been vigorously developed. The MR sensor and head read an external magnetic signal through the resistance change in a reading sensor part comprising a magnetic material. Since a relative speed of the MR sensor or head with a magnetic recording medium does not depend on a reproducing output, a high sensitivity is achieved by the MR sensor and a high output is obtained by the MR head even in case of a high density magnetic recording.
However, with a MR sensor which comprises a conventional magnetic substance utilizing anisotropic magnetoresistance effect such as Ni.sub.0.8 Fe.sub.0.2, a magnetoresistance ratio .DELTA.R/R (which will be defined below) is only about 2 to 5%. Then, a MR element having a larger magnetoresistance ratio is desired.
Recently, it was found that an artificial superlattice film in which directions of magnetization in adjacent magnetic layers are opposite such as Fe/Cr!.sub.N induces a large magnetoresistance effect (Phys. Rev. Lett., 61, 2472 (1988)). However, with this artificial superlattice film, an external magnetic field at which the maximum resistance change is achieved is very large, namely from ten several KOe to several ten KOe. Therefore, this artificial lattice film as such cannot be practically used.
As described above, the conventional MR sensor and head have a small resistance change, and the conventional artificial superlattices such as Fe/Cr require too large external magnetic field to induce the resistance change.
The present inventors invented, as a magnetoresistance effect element which solves the above problems, a magnetoresistance effect element comprising a substrate and at least two magnetic thin layers which are laminated with interposing a non-magnetic thin layer therebetween on said substrate, wherein adjacent magnetic thin layers through the non-magnetic thin layer have different coercive forces, and filed the patent applications (Japanese Patent Application No. 3-78824 and PCT/JP91/00671 (WO91/18424) corresponding to U.S. Ser. No. 07/820,866 and EP-A-0 483 373).
However, since the magnetoresistance effect element of the above prior application has insufficient smoothness of each layer, when a thickness of the non-magnetic thin layer is reduced, the resistance change is decreased and the mechanical strength is deteriorated.